This invention relates to methods and apparatus for effecting seals to prevent fluid leakage through thread clearances in tubular goods, and having particular utility for sealing joints in well pipes such as casing, tubing, drill pipe, and the like. More particularly, the present invention, in its more specific aspects, is directed to methods and apparatus for making and installing seals of the resilient plug type which may be installed adjacent the end of a threaded male pipe section into the outer surface thereof.
It has long been known that helical clearances occur in threaded pipe joints such as those employed in the oil and gas industry between the crests of the threads of one tubular member and the opposing recess space adjacent the thread roots of the other tubular member which threadedly receive these crests. These clearances are highly undesirable, permitting fluid leakage therethrough often due to commonly encountered high pressures within the pipe and the like. Numerous means have been employed in the past in an attempt to stop or minimize this leakage such as providing various thread designs which number well over fifty in oil and gas applications alone, for example. Further attempts to seal off these spaces have included coating the threads with an appropriate pipe dope in a manner well known to those familiar with the art. Other means have even included provision of various annular sealing rings, gaskets, or the like.
Yet an additional technique employed in attempts to solve the problem may be characterized by insertion into a transverse radial blind bore in the threads of one of the pipe joint sections of a resilient cylindrical disc or plug which deforms upon made up of the joint to fill the spiral clearance, thereby forming an element establishing a damming or sealing relation to prevent the aforesaid fluid leakage. Representative such pipe joint seals may be seen depicted in U.S. Pat. Nos. 2,631,871 and 2,474,556 to Stone.
Many problems have been associated with effecting to make up and installation of such cylindrical plug-type seals. First, it was necessary to establish the appropriate radial blind bore in one of the pipe sections. This bore must preferably be oriented a prescribed distance from the end of the pipe section and have uniform depth, circumference, and transverse orientation relative to the longitudinal axis of the pipe to receive a sealing plug having dimensional and compressional characteristics preselected to effect the desired sealing. Repeatedly, quickly, and uniformly establishing such precisely controlled counterbores, particularly in field conditions wherein jigs are not readily and conveniently available, proved to be difficult.
Moreover, assuming such a radial blind bore of the proper dimensions, orientation, and location has been established, insertion of an appropriate sealing plug in the bore so as to seat in proper alignment was further found to be time consuming and frequently difficult to achieve. Often such sealing plugs and the mating radial blind bores may preferably be of a relatively small nominal width, traversing only a few of the pipe threads. Accordingly, the sealing elements or plugs may, in like manner, be of a relatively small dimension rendering their handling difficult. Still further, inasmuch as the sealing element was preferably retained within the bore by means of a pressfit, proper installation and orientation of the plug within the radial blind bore was frequently found to be troublesome. Moreover, the separate repeated operations of fabricating the plug, drilling the counterbore, and inserting the plug were found to be quite tedious and time consuming. This was particularly the case wherein pipe sections and corresponding joints and seals numbering in the hundreds may be required as, for example, in a typical oil or gas well drilling or production operation.
With respect to the seal plugs themselves, it has been conventional to provide such plugs with preformed projecting lips or segments on the outer surface thereof or to cut such segments into the surface after installation of the plug but before make up of the pipe joint. It has been found that such approaches are often unsatisfactory requiring close tolelrances and failing to provide the desired degree of sealing such as in conditions of higher pressures.
It was thus highly desirable to provide methods and apparatus for effecting make up and installation of a plug-type seal with superior sealing characteristics wherein the operation could be reliably performed uniformly, simply, inexpensively, and with a minimum number of steps, and without the requirement for bulky apparatus, so as to facilitate installation of such seals in tubular goods wherein this feature may be desirable.